1. Technical Field
The present invention relates to a crystal device, in particular to a crystal device in which an electroconductive adhesive is used to fix a crystal piece to a container main body.
2. Background Art
A crystal device, for example a crystal oscillator, is known as a frequency controlling element, and is widely built into telecommunication equipment and digital controllers. As one of these, there is a crystal oscillator of a surface-mounted type (hereunder referred to as a surface-mounted oscillator) in which a crystal piece is fixed to a container main body using an electroconductive adhesive, and mass production of this is advancing.
(First Conventional Technique; Refer To Patent Document 1)
FIG. 13 and FIG. 14 are diagrams for explaining a surface-mounted oscillator of a first conventional technique, wherein FIG. 13(a) is a plan view of a crystal piece, FIG. 13(b) is a cross-sectional view on arrows A-A of FIG. 13(a), and FIG. 13(c) is a cross-sectional view on arrows B-B of FIG. 13(a), while FIG. 14 is a longitudinal cross-sectional view of the surface-mounted oscillator.
The surface-mounted oscillator 1 of the first conventional technique (refer to FIG. 14) is configured with a crystal piece 3A accommodated in a container main body 2 having a concavity 2e, and a cover 4 connected to an open end face of the container main body 2. The container main body 2 is made from ceramics, and is formed with a frame wall 2b laminated on a planar bottom wall 2a. On an inner bottom face 2c of the container main body 2 there is provided a crystal retention terminal 5. The crystal retention terminal 5 is electrically connected to a mount terminal 7 formed on an outer bottom face 2d of the container main body 2, via a conduction path 6.
The crystal piece 3A accommodated in the container main body 2 (refer to FIG. 13) is AT cut, and is an approximate rectangular shape in plan view with the longitudinal direction of the crystal piece 3A as the X axis. Furthermore, an excitation electrode 8 is formed on both main surfaces of the crystal piece 3A, and on both sides of one end portion in the longitudinal direction thereof, there is formed a support electrode 10 which is electrically connected to the excitation electrode 8 using a connection electrode 9. Moreover, on one main face of the crystal piece 3A there is formed a jetty 11 made from a silicone gum (heat curing silicone adhesive).
The jetty 11 comprises a first jetty component 12a that is formed between the support electrode 10 and the excitation electrode 8 along the full width in the widthwise direction of the crystal piece 3A, and a second jetty component 12b that extends from the centre of the first jetty component 12a to the periphery of one end portion of the crystal piece 3A on which the support electrode 10 is formed. In such a crystal piece 3A, the support electrode 10 is bonded to the crystal retention terminal 5 with an electroconductive adhesive 13 (refer to FIG. 14), and is thus fixed to the inner bottom face 2c of the container main body 2.
To the open end face of the container main body 2 there is connected a cover 4 for hermetically sealing the crystal piece 3A. The cover 4 is made from Kovar in which Fe (iron) is the main component to which is added Ni (nickel) and Co (cobalt). On the surface of the cover 4 there is formed a nickel film by means of for example electroplating. Furthermore, the cover 4 is connected for example to a metal ring (not shown in the figure) provided on the open end face of the container main body 2, by for example seam welding, so that the crystal piece 3A is hermetically sealed inside the container main body 2.
In such a device, since the jetty 11 made from an elastic material such as silicone gum is provided on one main face of the crystal piece 3A, flow out of the electroconductive adhesive 13 to the outside of the support electrode 10 can be prevented by a simple low cost process (refer to paragraph 0006 of Patent Document 1). By means of this jetty 11, influence on the vibration area formed by the excitation electrode 8, and contact of the electroconductive adhesive 13 between both sides of the one end portion is prevented, so that thickness-shear vibration is ensured giving good vibration characteristics.
(Second Conventional Technique, Refer To Patent Document 2)
FIG. 15 is a diagram for explaining a tuning fork type surface-mounted oscillator of a second conventional technique, wherein FIG. 15(a) is a plan view of a crystal piece, FIG. 15(b) is a cross-sectional view on arrows A-A of FIG. 15(a), and FIG. 15(c) is a cross-sectional view on arrows B-B of FIG. 15(a). Parts the same as in the first conventional technique are denoted by the same reference symbols and description thereof is simplified or omitted.
A crystal piece 3B used in the surface-mounted oscillator of the second conventional technique, as shown in FIG. 15, is formed in a tuning fork shape with a pair of vibrating arms 15 extended from one end portion of a base 14, being a so called tuning fork type oscillator. In the vibrating arms 15 there is formed a microgroove 16 for increasing the electric field strength, and in the microgroove 16 there is formed an excitation electrode 8. On both sides of the other end portion of the base 14 there is formed support electrodes 10 connected electrically to the excitation electrode 8 using a connection electrode (not shown in the figure). Furthermore, a jetty 11 is formed between the pair of support electrodes 10.
In such a device, when the crystal piece 3B is fixed in the concavity of the container main body (not shown in the figure), a situation where the electroconductive adhesive (not shown in the figure) flows out in a direction mutually approaching the pair of support electrodes 10, can be prevented by the jetty 11 (refer to paragraph 0039 in Patent Document 2). As a result, contact of the electroconductive adhesive 13 between both sides of the end portion is prevented, so that tuning fork vibration is ensured.
Prior Art Documents.
Patent Document 1: Japanese Unexamined Patent Publication No. 2007-96529
Patent Document 2: Japanese Unexamined Patent Publication No. 2003-152499